1. Field of the Invention
The present invention relates to a semiconductor device and, particularly, to a light emitting device having an organic light emitting element formed over a substrate having an insulating surface and a manufacturing method therefor. The present invention also relates to a module in which an IC etc. including a controller is mounted on a panel having the organic light emitting element. Note that, in this specification, the panel and the module which have the organic light emitting element are collectively referred to as a light emitting device. Further, the present invention relates to an apparatus for manufacturing the light emitting device.
Note that, in this specification, the term semiconductor device refers to the devices in general which can function by utilizing semiconductor characteristics. The light emitting device, an electro-optic device, a semiconductor circuit, and an electronic device are all included in the category of the semiconductor device.
2. Description of the Related Art
Techniques of forming TFTs (thin film transistors) on substrates have been progressing greatly in recent years, and developments in their application to active matrix display devices is advancing. In particular, TFTs that use polysilicon films have a higher electric field effect mobility (also referred to as mobility) than TFTs that use conventional amorphous silicon films, and therefore high speed operation is possible. Developments in performing control of pixels by forming driver circuits made from TFTs that use polysilicon films over a substrate on which the pixels are formed have therefore been flourishing. It has been expected that various advantages can be obtained by using active matrix display devices in which pixels and driver circuits are mounted on the same substrate, such as reductions in manufacturing cost, miniaturization of the display device, increases in yield, and increases in throughput.
Furthermore, research on active matrix light emitting devices using organic light emitting elements as self light emitting elements (hereinafter referred to simply as light emitting devices) has become more active. The light emitting devices are also referred to as organic EL displays (OELDs) and organic light emitting diodes (OLEDs).
TFT switching elements (hereinafter referred to as switching elements) are formed for each pixel in active matrix light emitting devices, and driver elements for performing electric current control using the switching TFTs (hereinafter referred to as electric current control TFTs) are operated, thus making EL layers (strictly speaking, light emitting layers) emit light. For example, a light emitting device disclosed in JP 10-189252 is known.
Organic light emitting elements are self light emitting, and therefore have high visibility. Backlights, necessary for liquid crystal display devices (LCDs), are not required for organic light emitting elements, which are optimal for making display devices thinner and have no limitations in viewing angle. Light emitting devices using organic light emitting elements are consequently being focused upon as substitutes for CRTs and LCDs.
Note that EL elements have a layer containing an organic compound in which luminescence develops by the addition of an electric field (Electro Luminescence) (hereinafter referred to as EL layer), an anode, and a cathode. There is light emission when returning to a base state from a singlet excitation state (fluorescence), and light emission when returning to a base state from a triplet excitation state (phosphorescence) in the organic compound layer, and it is possible to apply both types of light emission to light emitting devices manufactured by the manufacturing apparatus and film formation method of the present invention.
EL elements have a structure in which an EL layer is sandwiched between a pair of electrodes, and the EL layer normally has a laminate structure. A “hole transporting layer/light emitting layer/electron transporting layer” laminate structure can be given as a typical example. This structure has extremely high light emitting efficiency, and at present almost all light emitting devices undergoing research and development employ this structure.
Further, a structure in which: a hole injecting layer, a hole transporting layer, a light emitting layer, and an electron transporting layer are laminated in order on an anode; or a hole injecting layer, a hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injecting layer are laminated in order on an anode may also be used. Fluorescent pigments and the like may also be doped into the light emitting layers. Further, all of the layers may be formed by using low molecular weight materials, and all of the layers may be formed by using high molecular weight materials.
The conventional active matrix type light emitting device is composed of a light emitting element in which an electrode electrically connected with TFT on the substrate is formed as an anode, then the organic compound layer was formed on the anode. Light generated at the organic compound layer is radiated from the anode that is a transparent electrode to TFT.
However, in this structure, the problem has arisen when the resolution is intended to be risen that an aperture ratio is limited due to an arrangement of TFT and wirings in the pixel unit.